Reinforcement device with dissolvable layer and its use

ABSTRACT

A reinforcement device for reinforcing tissues having one or more structural deficiencies includes a longitudinally-extending reinforcing layer for treating the structural deficiency, a plurality of spiked naps distributed across the reinforcing layer and projecting therefrom for adhering to the tissue, and a dissolvable matrix layer covering at least a portion of the reinforcing layer and a portion of the plurality of spiked naps. The matrix layer increases the time before the spiked naps substantially adhere to the tissue, thereby allowing the practitioner additional time to position the reinforcement device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application No.13/859,406 filed Apr. 9, 2013, now U.S. Pat. No. 8,968,418, which is adivisional of U.S. patent application No. 12/783,936 filed May 20, 2010,now U.S. Pat. No. 8,435,307, and the disclosures of each of theabove-identified applications are hereby incorporated by reference intheir entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates generally to abdominal wall reinforcementdevices, and in particular devices used for the treatment of inguinalhernias by either an anterior or laparoscopic route.

2. Description of the Related Art

Providing a permanent mechanical support for the repair of abdominalwall hernias is well known in the art. Various implants and surgicaltechniques have been developed to assist surgeons during reconstructiveprocedures to improve the outcome of such procedures, both in terms ofits effectiveness and tolerance by the patient. It is known, forexample, that reinforcement of the operative area by a mechanicalimplant is improved when the implant quickly integrates in the tissue.As disclosed in U.S. Pat. No. 6,596,002 (assigned to Sofradim), toachieve intimate and early integration of the implant without formationof a peripheral fibrous shell, the macroporosities of the implant mustbe as widely open as possible to the outside and the elasticity of thereinforcement must allow it to follow the physiological deformations ofthe wall onto which the device is placed. The suitability of such adevice is related to the mechanical resistance of the textile materialused to form the implant. It is reported that such resistance must begreater than 10 decanewtons using the standardized ISO5081 test. Suchdevices should prevent hernia recurrence through the pores of thetissue, which must be a maximum of 7 to 10 millimeters in diameter.

The invention disclosed in U.S. Pat. No. 6,596,002, involves a knittedmesh useful for the treatment of inguinal hernias by the anterior accessroute, which is placed in a premuscular location. The knitted mesh ischaracterized as affording the practitioner with an implant device thatis easy to use, quickly securable in place, and that effectively repairsabdominal wall deficiencies. The knitted mesh includes a reinforcementpiece and a flap piece connected to the reinforcement piece. Thereinforcement piece is cut from an open-worked prosthetic knit web. Theweb is made of multifilament yarns. The reinforcement piece includes aradial slit and annular cut-out region approximately in the center ofthe reinforcement piece that allows the surgeon to place the piecearound the spermatic cord. According to the patent, the reinforcementpiece has the general shape of an ellipse, and it satisfies therequirements mentioned above. In particular, the shape allows thesurgeon to cover all the potential parietal weakness. The device isdescribed as being easy to put into place.

The aforementioned flap piece is made such that it may be folded overthe slit on the reinforcement piece to close it. The flap is describedas having a “gripping means” integral with the flap itself, or attachedto it, for fastening or joining the flap piece to the knitted structureof the reinforcement piece. In one embodiment, the flap is described ashaving spike naps projecting from its face. The spiked naps are formedby a monofilament yarn and have a length allowing them to penetrate intoand attach themselves to the knitted structure of the reinforcementpiece without protruding from the latter. That is, on one end, thespiked naps are embedded into the knit web to secure them, and on theother end project above the surface of the flap piece, generallyextending above the plane of the flap piece in a perpendiculardirection. Depending on the particular applications for the device, thespike naps are made of a biocompatible polymer or of bioabsorbablematerial, such as polylactic acid (PLA). In use, the flap is folded overthe reinforcement piece such that the spiked naps engage in and betweenthe multifilament yarns of the knit of the reinforcement piece, similarto a hook and loop fastener. This ensures that the flap piece is lockedin position, securely closing the slit and holding the spermatic cord inposition. The spiked naps are not permanent, however. The flap piece maybe unfastened and repositioned, if necessary.

The density of the spiked naps is reportedly determined as a function ofthe prosthetic knit being used, but is reportedly best in the range ofbetween 50 and 90 naps per cm². The length of the naps, measured fromthe base projecting from the attachment sheet to the top of the spike,will depend on the thickness of the prosthetic knit forming thereinforcement piece, but is reportedly best in the range between 1 and 2millimeters.

In the aforementioned patent, the reinforcement piece is described ashaving a grip or gripping means, which is integral with the knit orattached to it, and is used for fastening or joining The same spikednaps described above may be used on one face of the reinforcement piece,just as they are used on the flap piece. The grip/gripping means devicesproject from one and/or the other of the faces of the knit, and are usedto fasten or join the reinforcement piece to the tissues the device isplace in contact with. The knit from which the reinforcement piece ismade is described as a “flat knit” type or one having two porous layersconnected by connecting yarns. The weave of the knit forms run-prooftransverse channels opening out from the two porous layers.

A commercial embodiment of the knitted mesh device called ProGrip™ isavailable from Covidien (Massachusetts). Its use is described inPhilippe Chastan, M.D., “Tension-Free Open Inguinal Hernia Repair Usingan Innovative Self Gripping Semi-Resorbable Mesh,” published in theJournal of Minimal Access Surgery, 2006 (see pp 139-43 describingresults based on a published study of the Parietene™ (polypropylene)version of the ProGrip™). In its literature, Covidien states that thebiocompatible monofilament knit making up the knitted mesh is made fromnon-resorbable polyethylene teraphthalate (PET), and the spike naps aremade from a resorbable poly lactic acid (PLA). The monofilament knit ishydrophilic, so it works with the body's natural systems to improvetissue integration while reducing foreign material response. The entiremesh with the spike naps reportedly provides “immediate fixation” to theunderlying tissue. The knit material is substantially stronger thanusing fibrin glue, and is equivalent to incorporation by hernia staplerfixation at five days after placement. Compared to suture fixation, thedevice is 100% stronger at four weeks. The literature also notes thatthe device can be positioned and placed in less than 60 seconds, andunlike standard open repair of parietal deficiencies, the device doesnot require additional fixation methods. The device has a reporteddensity of 73.0 g/m² before resorption of the spiked naps, and areported density of 38.0 g/m² after resorption (a change of 53 g/m² or48-percent).

Despite the features and advantages of the invention described above,experience has shown that the spike naps may adhere too quickly for someapplications, i.e., “immediate fixation” or adherence in less than 60seconds. Removing the device (so it can be repositioned) is difficultafter attachment, and it can be traumatic to the underlying tissue.Often, repositioning cannot be done, so a new device is requires, atrelatively substantial expense to the patient or practitioner. Also, thedevice is expected to attach quickly to intra-abdominal tissues (e.g.,smooth tissues such as bowel), and so the device is not useful forintra-abdominal implantation using, for example, laparoscopy instrumentsto place the device interiorly of, for example, an abdominal wallhernia. Accordingly, there exists a need for such a device.

It is well known in the medical arts to apply a measured amount of aspreadable “gel” to form a temporary layer, which may then provide thebenefit of protecting, at least temporarily, another layer, material, orobject, or to reduce the friction between two surfaces separated by thegel layer. Such a gel, if applied to the spiked naps of theaforementioned product, would reduce the gripping ability of the spikednaps and allow the practitioner to place and then replace the knittedmesh device before the spiked naps begin to adhere to the parietaltissues. However, if the gel has a high viscosity, the ability of thespiked naps to be reabsorbed by the underlying tissue may be greatlyreduced, causing the knitted mesh to be too loose and require additionalsutures. Also, low viscous gels are unsuitable from a manufacturingperspective, because they are difficult to apply to a mesh, and wouldrequire special or different packaging materials compared to a knittedmesh without a gel layer. Further, many gels may be easily disturbed bythe practitioner's fingers and/or instruments used by the practitioner,thereby reducing or eliminating their effectiveness.

It is also well known in the medical arts to use adhesives to attached adevice to a patient or substrate. An adhesive layer applies to theknitted mesh and/or spiked naps of the aforementioned device wouldimmediately cause fixation, making it more difficult to remove orreposition. Also, unlike the spiked naps of the aforementioned knittedmesh device, an adhesive is generally not reabsorbed (at least notimmediately), and so it can form (at least temporarily) a generallyimpenetrable layer between the device and the underlying tissue, whichmay not be desirable in certain applications.

It is also known in the medical arts to use a removable, protective filmor layer over another layer. Thus, a film could be used over an adhesivelayer on a device that prevents the adhesive from sticking until thedevice is used. Such protective films are relatively inexpensive to makefrom various inert, compatible, and stable polymeric materials. In use,the practitioner simply removes and discards the film, then positionsthe device and permanently places it using the underlying adhesive tohold the device in place. Adding a film to an adhesive layer may befeasible, but it may not be suitable for adding directly to the knittedmesh device described above without at least some adhesive between thefile and underlying PET knit and PLA spiked naps extending from theknit. If the film attaches to the spiked naps, it may not be cleanlyremovable without destroying some of the spiked naps, thereby reducingthe effectiveness of those devices for their intended purpose. Also,removing the film intra-abdominally presents all sorts of challenges tothe practitioner and is, practically speaking, not feasible (i.e., thefilm would have to be removed exteriorly of the patient).

Accordingly, there exists a need for a material that reduces the timebefore the spiked naps of the aforementioned invention begins to adhereand reabsorb in the tissue so that it can be removed and repositionedquickly, is suitable for manual placement by a practitioner's fingers orusing a laparoscopy instrument, and is relatively inexpensive tomanufacture.

SUMMARY AND OBJECTS OF THE INVENTION

Accordingly, it is a principal object of the present invention toprovide a reinforcing device for effective parietal hernia repair andother reconstructive tissue repairs that can be positioned by apractitioner using an anterior route as well and a laparoscopic route.

It is also an object of the invention to provide a reinforcing devicethat is suitable for placement in an intra-abdominal or intra-pelviclocation using a laparoscopic device that does not require conventionalsutures or staples.

It is still another object of the invention to provide a reinforcingdevice made from a knitted mesh having spiked naps in which at least aportion or all of the knitted mesh and spiked naps on one of the facesof the device are covered with a layer that is dissolvable in arate-controlling manner.

It is another object of the invention to provide a dissolvable materialthat may be coated on a monofilament strand of PET and/or a spiked napof PLA to a pre-determined thickness and that dissolves at apre-determine rate from the outer contact surface exposed to varioussolvents.

It is still another object of the invention to include a formulation fora dissolvable matrix having one or more of a biodegradable component, anantibacterial component, an excipient, a therapeutic drug, aplasticizer, and a binder component.

It is another object of the invention to provide a device that isrelatively easy for a practitioner to use.

It is still another object of the invention to provide a device that isrelatively easy to manufacture.

Briefly described, the above and other objects and advantages of thepresent invention are accomplished, as embodied and fully describedherein, by a reinforcement device for reinforcing tissues having one ormore structural deficiencies, such as parietal tissues. The deviceincludes a longitudinally-extending reinforcing layer for treating thestructural deficiency, the layer having an upper and a lower face, aflap portion, a slit portion, and a cut-out portion; a plurality ofspiked naps distributed across one or both of the faces and the flapportion and projecting therefrom for adhering to the tissue; and a firstdissolvable matrix layer covering at least a portion of the reinforcinglayer and a portion of the plurality of spiked naps, the matrix layerincreasing the time before the spiked naps substantially adhere to thetissue.

The above and other objects and advantages of the present invention arealso accomplished, as embodied and fully described herein, by a methodfor reinforcing tissues having one or more structural deficiencies, thetreatment method including the steps of providing a reinforcement deviceas described above, and holding the reinforcement device at the tissueuntil at least a portion of the dissolvable matrix layer dissolves,allowing the device to adhere to the tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective schematic drawing of a reinforcing deviceaccording to the prior art;

FIG. 2 is a plan view of the reinforcing device of FIG. 1;

FIG. 3 is a partial cross-sectional elevation view of the reinforcingdevice according to one aspect of the present invention;

FIG. 4 is a partial cross-sectional elevation view of the reinforcingdevice according to another aspect of the present invention;

FIG. 5 is a plan view of the reinforcing device of FIG. 1 according toanother aspect of the present invention;

FIG. 6 is a partial cross-sectional view of section A-A of FIG. 5showing the partial coverage of the reinforcing device with adissolvable matrix layer and a bioadhesive layer;

FIG. 7 shows the change in the thickness, d (millimeters), of thedissolvable matrix layer over time; and

FIG. 8 is a partial cross-sectional view of a single spiked napaccording to one aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Several preferred embodiments of the present invention are described forillustrative purposes, it being understood that the invention may beembodied in other forms not specifically shown in the drawings. Thefigures will be described with respect to the structure and functionsthat achieve one or more of the objects of the invention and/or receivethe benefits derived from the advantages of the invention as set forthabove.

Turning first to FIG. 1, shown therein is a perspective schematicdrawing of a reinforcing device 102 according to the present invention.The reinforcing device 102 is made substantially in accordance with thedevice disclosed in U.S. Pat. No. 6,596,002, i.e., a knit whichsatisfies the requirements of the knits mentioned in the backgroundsection of the present description. Thus, the knit may bethree-dimensional and open-worked, with two porous faces connected byconnecting yarns.

The reinforcing device 102 has an upper face 104 and a lower face 106and is formed with a cut-out 108 approximately in the center of thereinforcing device 102 as shown. The cut-out 108 has a diameter of about3 to 7 millimeters.

The knit may be made of a monofilament yarn such as polyester, includingPET or similar materials. The knit is flexible, as depicted in FIG. 1,but it could also be made semi-rigid by coating or reacting the yarnwith a suitable polymer, plasticizer, or other material.

Turning now to FIG. 2, shown therein is a plan view of the reinforcingdevice 102 of the previous figure. As further disclosed in theaforementioned patent, which is incorporated herein by reference, thereinforcing device 102 is generally in the shape of an ellipse. Thisellipse includes a large radius of curvature on the upper and loweredges, and a smaller radius of curvature on the left and right edges,respectively. The reinforcing device 102 may be made to other shapes andsizes as needed. It is preferable that the specific edge shapecorrespond to one or more edges formed by the practitioner in a patientundergoing a procedure to place the reinforcing device 102. This willallow the device to be positioned in the best anatomical position inwhich it will remain after the procedure.

The reinforcing device 102 includes, about halfway along the length ofthe upper edge and extending from the cut-out 108 to the upper edge, anend portion 206, which is covered by a flap portion 202. The combinationof the flap portion 202 and the end portion 206 forms a slit or openingthat is generally perpendicular to the upper edge and parallel to theend portion 206.

Near one edge of the reinforcing device 102 is a cord 204 made from abiocompatible yarn material that is generally stronger than the rest ofthe material of the reinforcing device 102, and provides a suitableanchor for fixing a conventional suture or staple, if needed. Additionalcords 104 could also be added to the reinforcing device 102.

The flap portion 202 has may have the shape shown, i.e., rectilinearpolygon, or the shape of a sector of a circular annulus, or some othersuitable shape. It may also be a separate piece that is attached to thereinforcing device 102 at one of its linear or arcuate edges. The flapportion 202 extends over a portion of the upper face 104 of thereinforcing device 102 such that when it is joined to the reinforcingdevice 102 the lower edge is lined up with an edge of the cut-out 108.

As noted in the referenced patent, the flap portion 202 is composed ofan open-worked, run-proof knit made, for example, of multifilamentsynthetic yarns of polyester. In the case where the flap portion 202 isa separate piece, it may be joined or attached to the reinforcing device102 by a longitudinal stitch or seam that runs parallel to one of theedge of the end portion 206.

The knit used to make the flap portion 202 includes one or moremonofilament yarns forming spiked naps projecting from the flap portion202 or the lower face 106 of the reinforcing device 102 (and/or alsoprojecting from the upper face 104). Depending on the specific medicalapplication, the yarn for these spiked naps may be made of abiocompatible polymer. Suitable polymers include, but are not limitedto, polypropylene, or a bioabsorbable material. The bioabsorbablematerial may include, but is not limited to, polymers of p-dioxanone,polyglycolides, polyorthoesters, polymers of trimethylene carbonate,stereocopolymers of L-lactic acid and D-lactic acid, homopolymers ofL-lactic acid, copolymers of lactic acid and a compatible comonomer,such as derivatives of alpha-hydroxy acids.

Turning now to FIG. 3, shown therein is a partial cross-sectionalelevation view of the reinforcing device 102 according to one aspect ofthe present invention. Shown therein are several spiked naps 304,similar to those described above in connection with the flap portion202, projecting from the lower face 106 of the reinforcing device 102.Each of the spiked naps 304 has a length sufficient to penetrate intothe knit of the reinforcing device 102 (i.e., between the filaments ofthe yarns of the knitted structure of the reinforcing device 102). Ifthe knit making up the reinforcing device 102 has a thickness of between1.5 and 2.2 millimeters, as taught in the referenced patent, the lengthof the spiked naps 304 measured from their base, projecting from thelower face 106 to the summit of the spike could be between 1 and 2millimeters, as also taught in the referenced patent. The spiked naps304 do not have to be linear, and in fact may all have arcuate shapedelongated members terminating with an excess of the PLA materialgenerally in the shape of a flattened ball at the distal end of thespiked naps 304. The terminating end of the spiked naps 304 may alsohave other shapes, including, but not limited to, a tapered point orJ-hook shape.

The density of the spiked naps 304 depends on several factors, but isbased on the degree of adhesion required or desired for a particularapplication. Between 50 and 90 spiked naps 304 per square centimeter ofthe reinforcing device 102 is disclosed in the referenced patent and issuitable for most parietal reconstruction done from an anterior route. Alower or higher density may be suitable for other types of tissue andprocedures.

Covering substantially all of the spiked naps 304 is a dissolvablematrix layer 302 shown in the figure as a thin layer havingapproximately the same thickness as the reinforcing device 102, i.e.,about 1.5 to 2.2 millimeters, though other thicknesses may be used. Thedissolvable matrix layer 302 allows the reinforcing device 102 to floatas it is being positioned over an area of tissue so that the spiked naps304 do not immediately adhere to the underlying tissue. As thedissolvable matrix layer 302 dissolves, more of the spiked naps 304 areexposed allowing them to contact the tissue and begin to “adhere” byphysical and/or chemical means. The dissolvable matrix layer 302 mayextend across the entire lower face 106 (and/or the upper face 104) ofthe reinforcing device 102, or only a portion of the lower face 106 (orupper face 104).

The dissolvable matrix layer 302 may include one or more of abiodegradable component, an antibacterial component, an excipient, atherapeutic drug, a plasticizer, and a binder component. Otheringredients may also be included.

A variety of polymers are available for the biodegradable component.Suitable polyers include, but are not limited to, methyl cellulose (MC),hydoxy propyl methyl cellulose (HPMC) (commercially: hypromellose),hydroxyl propyl cellulose (HPC), starch and modified starch, Pullulan,Pectin, Gelatin, and carboxy methyl cellulose (CMC). The polymer shouldaccount for about 45-percent to 85-percent w/w of the total weight ofthe dissolvable matrix layer 302. The polymers identified above may beused alone or in combination to obtain the desired rate of mass transferfrom the layer to the surrounding. The polymers provide strength andresist damage while handling or during transportation in conventionalpackaging materials. The strength depends on the type of the polymer(s)and their relative amounts in the dissolvable matrix layer 302. Thepolymers are non-toxic, non-irritating, and lack leachable impurities.They have good wetting and spreadability properties, making themrelatively easy to use in various unit chemical operations such as spraycoating, fluidized reactors, pumping, etc. When in use (i.e., in a roomtemperature aqueous environment), they exhibit gel-like properties sincemost of the polymers are hydrophilic, and so they exhibit generally lowpeel strengths making them relatively easy to “float” over a substrate.In solid form, they exhibit good shear and tensile strengths andtherefore resist damage from medical instruments. Methyl cellulose inparticular can be used as a mild glue which can be washed away withwater.

An antibacterial component may optionally be included in the dissolvablematrix layer 302. A suitable non-toxic antibacterial agent includes, butis not limited to, silver ion powder (silver ions in an inertcrystalline material). The antibacterial component should account forabout 0 to about 5% w/w of the dissolvable matrix layer 302, thoughhigher percentages may be used. The antibacterial component in thedissolvable matrix layer 302 provides a germicidal effect that killsmicrobial organisms.

A therapeutic drug component may optionally be included in thedissolvable matrix layer 302. The amount of such component may bedetermined based on the desired dosage, i.e., a mass of drug to a bodymass ratio. The therapeutic drug component may be layered deep withinthe dissolvable matrix layer 302 to reduce loss after the reinforcingdevice 102 is placed in its final position and is washed (with a salineor water lavage), which can wash away the drug component. It may also beuniformly distributed within the dissolvable matrix layer 302. The drugcomponent can be added to the dissolvable matrix layer 302 as a milled,micronized, nanocrystal, or macro particle, depending upon the releaseprofile desired.

A plasticizer may optionally be included in the dissolvable matrix layer302. Suitable plasticizers include glycerol, propylene glycol, lowmolecular weight polyethylene glycols, phthalate derivatives likedimethyl, diethyl and dibutyl phthalate, citrate derivatives such astributyl, triethyl, acetyl citrate, triacetin and castor oil are some ofthe commonly used plasticizers used in dissolvable matrices like oraldissolvable strips. The plasticizers account for about 0 to about20-percent w/w of the dry polymer weight, though a higher percentage maybe used. The plasticizers improve the handling properties of the polymerand provide flexibility and reduce the brittleness of the dissolvablematrix layer 302. Other advantages of plasticizers for use indissolvable layers are discussed in Dixit et al., “Oral StripTechnology: Overview and Future Potential,” J. Controlled Release, 139:94-107 (2009), the content of which is incorporated herein in itsentirety.

An optional binder may also be included in the dissolvable matrix layer302. Suitable non-toxic binders are well known in the controlled releasearts. The amount of binder will depend upon the desired rate ofdissolution.

Turning now to FIG. 4, shown therein is a partial cross-sectionalelevation view of the reinforcing device 102 according to another aspectof the present invention. In the embodiment shown, a bioadhesive layer402 may added between the knitted mesh of the reinforcing device 102 andthe dissolvable matrix layer 302 such that when the dissolvable matrixlayer 302 is removed, the bioadhesive layer is exposed and attaches oradheres to the underlying tissue. The bioadhesive layer 402 may have avariable thickness across the width of the reinforcing device 102, andin another embodiment, only a portion of the knitted mesh is layeredwith the bioadhesive layer 402. As shown in the figure, it has athickness of about half or two-thirds of the thickness of thedissolvable matrix layer 302, but the actual layer can be determinedbased on the specific application in which the reinforcing device 102 isused. The bioadhesive layer 402 is a natural polymeric materials thatact as an adhesive, and may be dissolvable or resistant to dissolving(fixed thickness), and, as noted above, is used to supplement theadhesive function of the spiked naps 304 of the reinforcing device 102.Suitable bioadhesives include gelatin, starch, modified starch, certainproteins, carbohydrates, glycoproteins, and mucopolysaccharides, andhydrogels, which can simulate natural tissue.

One of ordinary skill in the art will appreciate that other layers, orcombinations of layers, and their position on the reinforcing device102, may be used for a particular application. For example, in FIG. 5the dissolvable matrix layer 302 is shown applied to discrete locationson the reinforcing device 102. Two of the locations are the left andright ends of the device, and the other location is concentric with thecut-out 108. FIG. 6 is a partial cross-sectional view of section A-A(FIG. 5), showing the partial coverage of the reinforcing device 102with the dissolvable matrix layer 302, and a bioadhesive layer 402,which may be slowly or rapidly dissolvable. The dissolvable matrix layer302 could be interchanged with the bioadhesive layer 402 in theembodiment shown, such that the dissolvable matrix layer 302 covers thebioadhesive layer 402.

The dissolvable matrix layer 302 is dissolvable according to apre-determined, controlled rate, which may be adjusted by usingdifferent ingredients or different concentrations of the sameingredients, or by using different solvents or combinations of solvents.Well known mass transfer principles may be used to describe the rate atwhich the layer dissolves (i.e., convective and diffusive degradation atthe solid-liquid interface). FIG. 7 shows the change in the thickness, d(millimeters), of the dissolvable matrix layer 302 over time. Each ofthe lines shown has a different first- or higher-order dissolution rateover time. Line 702, for example, represents a constant or first-ordermass transfer rate at the surface of the dissolvable matrix layer 302(transfer of solid to a surrounding convective fluid layer at thesurface, i.e., the fluid provided by the practitioner as a water lavagewhen the device is positioned, and/or provided by natural bodily fluidsat the site of the reinforcing device 102). Line 704 includes twodifferent rates, 704 a and 704 b, each with a different rate of masstransfer. Line 706 represents a variable rate of mass transfer, which israpid initially. Line 708 represents a low rate of mass transfer,whereby the thickness, d, changes slowly over time. Once the dissolvablematrix layer 304 is reduced by about 50-percent, most of the terminalends of the spiked naps 304 will be exposed.

FIG. 8 is a partial cross-sectional view of a single spiked nap 304having an elongated member 804 and terminating end 802. The spiked nap304 is shown coated with the dissolvable matrix layer 302 having athickness, d (millimeters). Since the spiked nap 304 thus coated withthe dissolvable matrix layer 302 may extend farther into a bulk fluid(e.g., solvent, such as water), the rate at which the thickness, d,changes over time may be greater than the layer 302 covering the knit ofthe reinforcing device 102 because of the increased prominence ofconvective mass transfer compared to diffusive mass transfer closer tothe surface of the reinforcing device 102.

In use, the reinforcing device 102 with the dissolvable matrix layer 302is removed from its packaging material. In the case where a thin filmcovers the dissolvable matrix layer 302, it is removed by thepractitioner prior to use. In a conventional procedure to treat aninguinal hernia, the device is positioned in the anterior inguinalregion of a patient and then the area is wetted with a water lavage (orsome other solvent is used), which maintains a constant moisture sourceand helps dissolve the dissolvable matrix layer 302. Dissolution occursfrom both sides of the dissolvable matrix layer 302. The anteriorsurface closest to the knitted mesh of the reinforcing device 102 isdissolved by the solvent as it penetrates the mess. The opposite surfaceis dissolved by the solvent as it penetrates from the sides of thereinforcing device 102, between the space between the dissolvable matrixlayer 302 and the underlying tissue, and by bodily fluids present at thesite.

Depending on the thickness of the dissolvable matrix layer 302 or itscomposition, the spiked naps 304 will begin to be exposed and contactthe underlying tissue, at which time they will begin to adhere to thetissue. Without the dissolvable matrix layer 302, the reinforcing device102 attaches almost immediately, but at least within about 30 seconds.Thus, the time until substantial attachment or adherence is in the rangeof about 0 to 30 seconds, which is increased with the dissolvable matrixlayer 302, such that substantial attachment occurs in a range from about30 seconds to several minutes, depending, again, on the thickness andcomposition of the dissolvable matrix layer, and the amount and flowrate of the solvent.

Substantial attachment or adherence is measured in terms of peelstrength, i.e., the force, measure in pounds or Newtons per area,required to remove the reinforcing device 102 after its placement ontissue after a pre-determined time period. This parameter is measurable;for example, the peel strength of two objects (one flexible, one rigid)joined together is the average load per unit width of bond line requiredto part the bonded materials from each other where the angle ofseparation is 180 degrees and separation rate is 6 in/min (AS™ D-903).

Preferably, the “float” period (i.e., the period before substantialadhesion) according to the present invention is from about 1 to 2minutes at a peel strength of about 1 to about 3 N/cm, but a much lowerpeel strength may be desired. That is, when wetted, the dissolvablematrix layer 302 may form a gel that reduces the ability of the spikednaps 304 to adhere and become resorbable. This provides the practitionersufficient time to assess the initial placement of the reinforcingdevice 102 and reposition the device as needed before adhesion begins. Afaster adhesion would create a higher peel strength and would likelycause trauma to the underlying tissue and damage the reinforcing device102 if attempts to remove it at that point were to occur.

Although certain presently preferred embodiments of the disclosedinvention have been specifically described herein, it will be apparentto those skilled in the art to which the invention pertains thatvariations and modifications of the various embodiments shown anddescribed herein may be made without departing from the spirit and scopeof the invention. Accordingly, it is intended that the invention belimited only to the extent required by the appended claims and theapplicable rules of law.

I claim:
 1. A reinforcement device for reinforcing tissues having one ormore structural deficiencies, comprising: a longitudinally extendingreinforcing layer for treating the structural deficiency, the layerhaving a first face and a second face; a plurality of naps distributedacross at least the first face and projecting therefrom for adhering totissue; and a dissolvable layer covering the plurality of naps, thelayer adapted to increase the time before the naps substantially adhereto the tissue.
 2. The device of claim 1, wherein the reinforcing layercomprises a three-dimensional and open-worked, porous knit.
 3. Thedevice of claim 2, wherein the knit comprises a monofilament polyesteryarn.
 4. The device of claim 1, wherein the naps comprise abiocompatible polymer.
 5. The device of claim 4, wherein thebiocompatible polymer is selected from one or more of polypropylene,polymers of p-dioxanone, polyglycolides, polyorthoesters, polymers oftrimethylene carbonate, stereocopolymers of L-lactic acid and D-lacticacid, homopolymers of L-lactic acid, copolymers of lactic acid and acompatible comonomer.
 6. The device of claim 1, wherein the dissolvablelayer comprises one or more of a biodegradable component, anantibacterial component, an excipient, a therapeutic drug, aplasticizer, and a binder component.
 7. The device of claim 6, whereinthe biodegradable component is a polymer selected from hydroxy propylmethyl cellulose, hydroxyl propyl cellulose, starch and modified starch,pullulan, pectin, gelatin, and carboxy methyl cellulose.
 8. The deviceof claim 7, wherein the amount of the polymer is about 45 percent w/w ofthe total weight of the dissolvable layer.
 9. The device of claim 6,wherein the antibacterial component comprises a non-toxic antibacterialagent.
 10. The device of claim 9, wherein the amount of theantibacterial component is from about 0 to about 5% w/w of thedissolvable layer.
 11. The device of claim 6, wherein the therapeuticdrug component is uniformly distributed in the dissolvable layer. 12.The device of claim 6, wherein the plasticizer is selected from one ormore of glycerol, propylene glycol, low molecular weight polyethyleneglycols, phthalate derivatives like dimethyl, diethyl and dibutylphthalate, and citrate derivatives such as tributyl, triethyl, acetylcitrate, triacetin and castor oil.
 13. The device of claim 1, furthercomprising a bioadhesive layer.
 14. The device of claim 13, wherein thebioadhesive layer comprises one or more of gelatin, starch, modifiedstarch, proteins, carbohydrates, glycoproteins, mucopolysaccharides, andhydrogels.
 15. The device of claim 1, wherein an individual nap has acoating of the dissolvable layer of a defined thickness, the thicknessof the coating changing over time at a rate greater than the dissolvablelayer.